Maxwell’s unified description of electric and magnetic phenomena is one of the greatest achievements of 19th century physics. Free magnetic charges and currents are not allowed in Maxwell’s equations, a consequence of their apparent absence in Nature. However, their existence would naturally explain the quantization of electric charge, as first noted by Dirac in 1931.

Cosmic rays are energetic particles, mostly atomic nuclei, raining down upon the Earth from the depths of the cosmos. Understanding their detailed nature and origins remains a primary goal in modern-day astroparticle physics.